"Mercury, also known as quicksilver, remains liquid at room temperature and is a beautiful and graceful metal. Unfortunately it is also extremely toxic. For many years the world's greatest source of mercury was the mercury mines at Almadén, Spain, which produced some 250,000 metric tons of mercury over the last 2,000 years in operation. So when Spain decided to built a monument to the mine (which was worked by criminals and slave labor most of whom died of mercury poisoning) they commissioned American sculptor Alexander Calder to build them a beautiful fountain which instead of pumping water, pumped pure mercury. It was to be displayed at the 1937 World's Fair." - Steven Perez from Bookmarklet